Squid giant axons will be subjected to repetitive stimulation at various frequencies while the light absorption from calcium arsenazo previously injected in the fiber is followed. Such measurements will be made with multi-channel spectrophotometry so that it is possible to follow not only the concentration of ionized calcium in the fiber but also possible concurrent changes in hydrogen ion concentration using a pH indicator for this purpose. There are reasons for believing that the entry of large amounts of calcium associated with bioelectric activity stimulate mitochondria to take up this entering calcium and that such mitochondria do so in exchange for hydrogen ions which can be measurable given the present sensitivity of pH indicators and spectophotometry. Upon cessation of bioelectric activity it is known that such stimulated nerve fibers lose calcium (both ionized and analytical) and hence one can expect to observe the reversal of both the calcium ion changes and hydrogen ion changes that are postulated to occur in the sentence above.